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Homework Help: Energy supplied by circuit

  1. Aug 24, 2009 #1
    1. The problem statement, all variables and given/known data

    For the element shown below, v(t) = ½ t Volts and i(t) = 12t-4t2 Amps.

    a)Find the instantaneous power p(t) as a function of time.

    b)Find the energy supplied (this value can be negative or positive for each range) to the element for the following three time ranges:

    0 < t < 3, 3 < t < 4, 0 < t < 4, those are less than or equal to.

    2. Relevant equations

    There is a picture of the circuit that show that it satisfies the Passive Sign Convention.

    P(t) = V(t) i(t)

    w= the integral of P(t)

    3. The attempt at a solution

    for part a. I multiplied the given V times the i and found p(t) to = 6t^2 - 2t^3 watts.

    for part b. I attempted to take the integral of P(t) from the first point listed; 0 < t < 3

    I dont understand the integration. Do i integrate from infinitie to 0, then from 0 to 3, and then from 3 to infinitie?? im so lost at this point.
  2. jcsd
  3. Aug 24, 2009 #2


    User Avatar
    Homework Helper

    Re: Physics/Circuits

    Just integrate form 0 to 3

    EDIT: also if you have infinity in the limits, the polynomial will tend to infinity as t→ inf.
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